1. Field of the Invention
The present invention relates to an optical pickup device which is thinner than conventional ones. The optical pickup device of the present invention is suitably mounted on a notebook-sized personal computer particularly demanding a thin optical pickup device.
2. Description of Related Art
FIGS. 9A to 9C are top views showing a structure of a conventional optical pickup device adapted to a plurality of different recording media such as CD and DVD. FIGS. 10A to 10C are enlarged views of a portion of a turning mirror in the conventional optical pickup device.
The optical pickup device comprises, as shown in FIGS. 9A to 9C, two light sources 1 and 2 having different wavelengths, a beam splitter 3 for adjusting the optical axes of light beams generated by the light sources 1 and 2 to coincide, a collimate lens 4 for converting the beams into parallel beams, a turning mirror 5 for turning the optical axis of the parallel beams by about 90 degrees, an opening-regulating filter 6 having a flat plate shape and wavelength selectivity, and an objective lens 8 for forming a condensed beam spot on a data surface of an optical information disc to record, reproduce and erase data.
As described in JP-A 11-161997 (1999), the opening-regulating filter 6 is disposed immediately below the objective lens 8 in a lens holder 7 to obtain an optimum condensed beam spot in each of a plurality of kinds of media for beams with different wavelengths and having different substrate thicknesses by using a single objective lens 8.
The holder 7 for holding the objective lens 8 is supported by elastic members 14 forming a parallel link and is controlled by a focusing mechanism (height direction) (not shown) and a tracking mechanism (radial direction of an optical information disc) (not shown) so that a condensed spot is continuously formed on a data surface, even when there occurs decentering or a face run-out of the optical information disc.
In particular, in DVD and following discs of recent years, as the packing density and precision of an optical information disc is becoming higher, it is necessary to condense a light beam to an extremely small spot. An optical system in which the wavelength of a laser beam is shortened to 670 nm or less and the numerical aperture (N.A.) of the objective lens is set to 0.6 or larger is employed.
The size of coma aberration which occurs in a condensed beam spot is proportional to the third power of the numerical aperture of the objective lens 8, the size of astigmatism is proportional to the square of the numerical aperture of the objective lens 8, and both of them are proportional to the inverse of the wavelength. Consequently, there is a problem such that the influence of the tilt of an optical information disc becomes serious due to shortening of the wavelength and increase in the numerical aperture.
In order to solve the problem, an objective lens tilting mechanism (not shown) is employed to tilt the objective lens 8 in the same direction as the tilt of an optical information disc to maintain a small aberration of a condensed beam spot.
In the high-precision optical pickup device of this kind, to obtain a required fine condensed spot, usually, optical glass or crystal member is used for both of the opening-regulating filter 6 and the turning mirror 5 from the viewpoint of precision.
As understood from the enlarged views of FIGS. 10A to 10C, to reduce the thickness of the optical pickup device, it is sufficient to reduce the interval between the turning mirror 5 and the opening-regulating filter 6. However, when the interval is narrowed, both of the parts may come into contact with each other, for example, in the case such that spontaneous disturbance occurs in lens position control or a spot is forcedly condensed on an optical information disc which is out of specification. In this case, a problem occurs such as break, chipping, or irregularity in mounting precision.
In order to solve the problem, a mechanism is employed which prevents the turning mirror 5 and the opening-regulating filter 6 from coming into contact with each other by providing a stopper 9 for the holder 7 and providing a stopper receiver 11 for a housing 10 as a casing of the optical pickup. Another embodiment of the stopper receiver is disclosed in JP-A 2001-319342.
The conventional stopper 9 is usually provided at each of two corners of the holder 7 as shown in FIGS. 10A to 10C. Consequently, a height space expressed by (h)=(W/2)SIN(θ) where (θ) denotes the angle of tilt by tilting operation and W denotes width of the holder 7 is necessary, and it hinders reduction in thickness of the optical pickup device.